Since 2014, carbon taxes have been spreading in South America. Counterintuitively, while they are primarily considered climate policies, their adoption has been largely driven by causes unrelated to the reduction of greenhouse gas emissions. The carbon tax policymaking literature has overlooked the causes that trigger the causal mechanisms for adopting carbon taxes and has instead centered on parts of the causal mechanism. Focusing on the very beginning of the process, namely the causes triggering the decision to pursue carbon taxes in Argentina and Uruguay, this study both contributes to the carbon tax policymaking literature and to the burgeoning application of logical Bayesian analysis in qualitative studies. According to previous studies, the pursuit of carbon taxes inherently entails political challenges linked, among others, to its potential regressive impacts and effects on industries, which makes the sudden rise of carbon taxes in Argentina and Uruguay surprising. Based on 26 expert interviews and a desk review, the study applies a logical Bayesian analysis to study potential causes structured around mutually exclusive hypotheses consistent with the carbon tax policymaking literature. It shows that the causes for pursuing carbon taxes in Argentina and Uruguay are not primarily related to mitigation. Instead, Argentina conceived carbon taxation as part of a broader reform of